Apple Watch didn’t detect my fall

I fell last night - passed out due to drop in blood pressure and dropped to the floor - unfortunately face first fracturing some teeth. My watch however did not notice that I had dropped to the floor suddenly or that I was laying there motionless. Any ideas why - and how do I ensure it does detect it in the future?

My my wife was there and she came running and made sure I was as ok as possible, but what if she wasn’t and it was more serious?

I had fall detection turned on - and I know it can’t detect everything 100% of the time as it’s only as good as the sensors and using them together, but a ‘dead’ fall like that I would have thought would have been one of the types of falls most easily recognizable.